Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $58.71   6.224%   $62.3641   $62.36   $62.35   $62.40  
  Purchase #2 $107.85   3.386%   $111.5018   $111.50   $111.50   $111.50  
  Purchase #3 $104.64   11.136%   $116.2927   $116.29   $116.30   $116.30  
  Purchase #4 $84.59   4.498%   $88.3949   $88.39   $88.40   $88.40  
  Purchase #5 $60.36   13.364%   $68.4265   $68.43   $68.45   $68.40  
  Purchase #6 $100.88   3.832%   $104.7457   $104.75   $104.75   $104.70  
  Purchase #7 $205.99   7.741%   $221.9357   $221.94   $221.95   $221.90  
  7 purchase totals = $723.02       $773.6614   $773.66   $773.70   $773.60